Abstract: Product yield and quality is increased during in situ retorting of oil shale by pulsed combustion in which the flow of feed gas to the flame front is intermittently stopped while continuously retorting the oil shale. A purge gas can be injected into the retort between pulses of feed gas to enhance transfer of sensible heat from the combustion zone to the retorting zone and enlarge the separation between the combustion zone and the advancing front of the retorting zone.

Abstract: An in situ process and ignition procedure are provided to retort oil shale which increases product yield and enhances uniformity of the flame front in an underground retort. In the process, a portion of the rubblized mass of oil shale is preheated with steam, nitrogen or some other inert gas, to at least the minimum oil shale ignition temperature and preferably retorted. Thereafter, the preheated oil shale is ignited with hot excess air or some other oxygen-containing gas above the maximum desired retorting temperature to establish a generally uniform flame front across the retort. In the preferred form, the preheating gas and oxygen-containing gas are introduced into the retort at different times from the same specially configured downhole burner.

Abstract: Solid hydrocarbon-containing material, such as oil shale, coal or tar sand, is fed into a retort through a multiplicity of feed lines to enhance retorting efficiency, throughput and product yield. In the preferred form, larger particles of hydrocarbon-containing material gravitate downwardly through the retort in countercurrent relationship to an upward fluidized stream of smaller particles of hydrocarbon-containing material. This arrangement is especially useful to retort larger particles of hydrocarbon-containing material. One or more streams of intermediate size particles of hydrocarbon-containing material can also be fed into the retort.